The present invention relates to a turbocharger for an internal combustion engine and, more particularly, to a motor-generator used with the turbocharger.
The output of an internal combustion engine is produced by combusting a mixture of fuel and air. To increase the engine output, it is necessary to introduce as much air as possible into the engine cylinders.
To meet the above requirement, internal combustion engines of today are equipped with a turbocharger having a turbine driven by the energy of an exhaust gas and an air compressor operatively coupled or integrally joined to the turbine. The air compressor is rotated by the turbine to charge a more-than-normal amount of air into the engine cylinders to burn the fuel efficiently. Therefore, the turbocharged internal combustion engine has an increased charging efficiency to produce a high output and a high torque while simultaneously achieving improved fuel consumption.
Although the conventional turbochargers can produce a large torque increase in medium and high speeds of rotation of the engine, the exhaust energy which tends to be excessive in high-speed and low-load engine conditions has to be discharged into the atmosphere. Under low-speed and high-load engine conditions, no sufficient exhaust energy is obtained and, hence, no sufficient air can be charged into the engine cylinders, with the result that the torque rises only slightly and no large freedom of selection of transmission gears is available. Therefore, the possibility of replacing large-size internal combustion engines with small-size turbocharged internal combustion engines is small though there is some improvement in the engine output. Where a small-size internal combustion engine is turbocharged for a greater engine output, it would be advantageous if the engine output could be increased without increasing the number of transmission gears by reducing a final gear ratio or increasing the mechanical strength of each gear. However, since the engine torque is low in low-speed engine rotation, the desired performance for the automobile to climp up a slope could not be achieved unless the transmission were altered to a large extent.
It has been proposed that the turbocharger be assisted by a generator in low-speed engine rotation, thereby increasing the air charging efficiency at the low engine speed. With this proposal, however, it is necessary to attach heavy windings, pole pieces, or permanent magnets to the driven component, thus increasing the rotational inertia thereof. As a consequence, the turbocharger will not function sufficiently.